My husband has a silent mind often too. Maybe it's a man thing? I ALWAYS have something going on in my mind. I'm chronically thinking, worrying, planning, imagining, stressing, rehearsing, memorizing, singing, etc.... You get the picture. But I do not have something repetitive and as consistently similar as you do. Could be harmless and just your "thing" but it might be interesting to bring up to a doctor and get their thoughts. Do you have OCD?